1. Field of the Invention
The present invention relates to a sealed prismatic battery and a battery module having a plurality of sealed prismatic batteries integrally connected to one another, and particularly to a sealed prismatic battery and a battery module with lower internal resistance.
2. Description of Related Art
A conventional battery module is constructed of a plurality of cells that are formed in the shape of a rectangular prism and connected to each other to provide the required power capacity. The cells are arranged such that the longer lateral walls of their battery cases are placed adjacent to each other. Those cells disposed at both ends in this arrangement are each provided with an end plate on the exterior of their respective cases and then united by restraining bands together. In each cell, leads extending upwardly from the top ends of electrode plates are connected to their respective terminals mounted in the lid of the battery case, with all the terminals of the cells being connected to each other via connection plates.
Accordingly, this arrangement has a long connection path and a number of connections between the cells, thereby causing a high resistance derived from their components including their connection components. This leads up to the proportion of 40 to 50% of the components' resistance to the reaction resistance caused by the electrochemical reaction between the positive and negative electrode plates and liquid electrolyte. This high internal resistance causes a large amount of heat to be generated in the cells. Consequently, there was an obstacle to implementation of high power output and improvement in the battery life characteristics. There was also another problem that a number of components were required for the connections increased in complexity between the cells, thereby adding cost to the battery module.
In light of these problems, the applicants of the present invention have proposed in the past a sealed prismatic battery module 1 having a plurality of cells 2 housed therein as shown in FIG. 9 and FIG. 10. The battery module 1 has a prismatic battery case 3 constructed in the shape of a flat rectangular prism in which cell cases 4 of the prismatic cells 2, each cell case having short lateral walls and long lateral walls, are coupled integrally to each other with the short lateral walls shared as partition walls 5. The open top ends of the cell cases 4 are covered with an integral lid 6. There are formed connection holes 7 in an upper portion of each partition wall 5 and in the short lateral walls of the cell cases 4 disposed at both ends of the battery module 1. Within each cell case 4, an electrode plate group 8 which has rectangular positive and negative electrode plates stacked upon one another with separators interposed in therebetween is accommodated in conjunction with a liquid electrolyte. The cells 2 are constructed in this manner. The positive and negative electrode plates in the electrode plate group 8 are protruded to the sides opposite to each other and serve as positive and negative electrode leads 9a, 9b, respectively, to the respective side edges of which collector plates 10a, 10b are connected by welding or the like.
In an upper part of the collector plate 10a, 10b, there is provided a connection boss 11 that fits into the connection hole 7, such that the connection bosses 11 of the positive and negative collector plates 10a, 10b are connected by welding to each other between adjacent cell cases 4, 4. On the outer short lateral walls of the cell cases 4 at both ends of the battery module, there are also provided positive and negative connection terminals (electrode pole) 12 in the connection holes 7, respectively, such that connection bosses 13 of the connection terminals 12 are connected by welding to the connection bosses 11 of the collector plates 10a, 10b, respectively. In this manners the plurality of cells 2 housed in the prismatic battery case 3 are connected to each other in series to provide power output between the connection terminals 12, 12 disposed at both ends of the prismatic battery case 3.
The construction as shown in FIGS. 9 and 10 provides a short current flow path from the positive and negative electrode plates to their respective leads 9a, 9b and collector plates 10a, 10b. However, as shown by the arrows in FIG. 11, since the Collector plates 10a, 10b are connected by welding to each other at a point between the tips of the connection bosses 11 provided at the upper end portions of the collector plates 10a, 10b, the connection path takes a detour thereby being elongated. Additionally, the connection bosses 11 are connected to each other at one location, thereby presenting a problem of providing a high internal resistance. What is worse, as shown by the hollow arrows, since the connection path takes a detour, a large amount of current flows through the electrode plate group 8 near the connection bosses of the collector plates 10a, 10b whereas a small amount of current flows therethrough away from the connection bosses This causes the electrode plate group 8 to provide an uneven distribution of current flowing therethrough and uneven power output, thus leading to power loss.